Method of forming shaped explosive charge



Sept. 16, 1958 N. A. M LEoD METHOD OF FORMING SHAPED EXPLOSIVE CHARGE Filed Jan. 18, 1954 INVENTOR. OZohnwwdWZaaW BY Qggf United States 2,851,918 Patented Sept. 16, 1958 METHOD OF FORlVIlNG SHAPED EXPLOSIVE CHARGE Norman A. MacLeod, Altadena, Calif.

Application January 18, 1954, Serial No. 404,819

3 Claims. (Cl. 86--1) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a method of casting a shaped charge of explosive, and of otherwise forming it to produce the most effective result.

In the casting of shaped charges from TNT or other thermoplastic explosive, it has been customary to pour the liquid explosive into a mold and to cool it from all surfaces equally to cause it to solidify. Because the mass was formed with a reentrant cavity, usually of conical form, this method of casting caused asymmetric crystal patterns which were not favorable to the formation of a uniformly advancing wave front upon detonation. Where the charge was made up of a mixture of two or more explosives, this method of casting favored segregation of the ingredients, particularly in the portion of the mass which was last to solidify. Also, vacuoles or small cavities tended to form in said portion, which destroyed the symmetry of the detonation wave.

In the present invention, the liquid explosive (which may be a mixture of different explosive materials) is poured into a mold in usual manner, but cooling takes place only, or chiefly, on the inner surface of the cavity. Byv this means, the crystal patterns which begin to form at the cavity surface may develop symmetrically without interference until they extend throughout the mass. The resulting charge is less likely to contain vacuoles and segrated masses, and the regularity of the detonation wave is correspondingly improved.

An object of the invention is to provide an improved method for forming a shaped charge.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following description.

Fig. 1 is a view in vertical section showing one manner of carrying out the invention;

Fig. 2 is a horizontal section taken on the line 22 of Fig. 1;

Fig. 3 is a view similar to Fig. 1, showing a modified manner of carrying out the invention; and

Fig. 4 is a view in elevation, partly in section, of a shaped charge made in accordance with the invention.

In the form of the invention shown in Figs. 1 and 2, represents a shaped charge which has been poured into a mold formed by a conical liner 12 and a cylindrical shell 14. Surrounding the shell 14 is a hollow cylinder 16, formed of heat insulating material. A cover or pad 18, also of heat insulating material, may be laid over the top of the charge after it has been poured, and separated therefrom by a metal plate 20. Water, air or other coolant is applied to the surface of the liner by means of a multiple jet 22, to hasten solidification of the charge adjacent the cavity.

In the operation of this form of the invention, the

molten explosive is poured into the insulated mold and covered with pad 18, and coolant is applied to the liner as above indicated. As a result, the crystal formations originating at the surface of the cavity develop without interference until they extend throughout the mass. If desired, the heat insulation may be replaced by material containing electrical resistance elements, to positively apply heat to the surfaces of the mass aside from the cavity surface.

In the form of the invention shown in Figs. 3 and 4, the mold is formed by the liner 12 and by a metal shell 30 of generally cylindrical form, having an inturned flange 32 upon which the liner rests. No heat insulation is used, but the cast mass exceeds in height and diameter the final dimensions of the charge, the shape of which is indicated by the dotted line 34. When the molten mass 36 has been poured, cooling proceeds rapidly adjacent the liner, which is cooled by means of jet 22, and slowly on the other surfaces. The resulting crystal growths originating at the cavity are indicated at 38, and meet the other crystal growths, indicated at 40, outside of the broken line 34. After the mass has solidified, it is machined to reduce it to the desired size, and thereby the irregular crystal formations, the segregated particles, and the voids or vacuoles formed at the meeting of the crystal growths are eliminated, and the remaining crystals are oriented symmetrically with respect to the lining surface and to the axis of the cavity.

The invention is applicable not only to charges having conical cavities, but also to those having cavities of hemispherical or other form.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. The method of forming a shaped charge, comprising delivering a mass of crystallizable molten explosive material to a closed cylindrical zone having a reentrant surface at one end thereof disposed symmetrically about the longitudinal axis of the charge, such as a conical surface having its apex on said axis, extracting heat from said surface while inhibiting extraction of heat across the remaining surfaces thereby effecting initial solidification and crystallization of the explosive in a zone substantially concentric with said surface, and continuing extracting heat from said surface while inhibiting extraction of heat across the remaining surfaces thereby effecting continuing solidification and crystallization uniformly in directions outwardly and away from said surface and until all of the explosive material has solidified and crystallized.

2. The method as defined by claim 1 wherein said initial crystallization is effected adjacent the outside surface of an explosive charge liner, through which the heat is extracted toward the interior surface thereof.

3. The method as defined by claim 2 wherein said interior surface is cooled by fluid coolant.

References Cited in the file of this patent UNITED STATES PATENTS 1,054,049 Sokolowski Feb. 25, 1913 1,231,388 Lake June 26, 1917 2,195,429 Shaler Apr. 2, 1940 2,314,378 Van Rossem Mar. 23, 1943 2,494,256 Muskat et al. Jan. 10, 1950 2,784,638 Diels et a1. Mar. 12, 1957 FOREIGN PATENTS 115,859 Great Britain May 30, 1918 

1. THE METHOD OF FORMING A SHAPED CHARGE, COMPRISING DELIVERING A MASS OF CRYSTALLIZABLE MOLTEN EXPLOSIVE MATERIAL TO A CLOSED CYLINDRICAL ZONE HAVING A RENTRANT SURFACE AT ONE END THEREOF DISPOSED SYMMETRICALLY ABOUT THE LONGITUDINAL AXIS OF THE CHARGE, SUCH AS A CONICAL SURFACE HAVING ITS APEX ON SAID AXIS, EXTRACTING HEAT FROM AND SURFACE WHILE INHIBITING EXTRACTION OF HEAT ACROSS THE REMAINING SURFACES THEREBY EFFECTING INITIAL SOLIDIFICATION AND CRYSTALLIZATION OF THE EXPLOSIVE IN A ZONE SUBSTANTIALLY CONCENTRATE WITH SAID SURFACE, AND CONTINUING EXTRACTING HEAT FROM SAID SURFACE WHILE INHIBITING EXTRACTION OF HEAT ACROSS THE REMAINING SURFACES THEREBY EFFECTING CONTINUING SOLIDIFICATION AND CRYSTALLIZATION UNIFORMLY IN DIRECTIONS OUTWARDLY AND AWAY FROM SAID SURFACE AND UNTIL ALL OF THE EXPLOSIVE MATERIAL HAS SOLDIFIED AND CRYSTALLIZED. 